I don't think the definition falls apart just because you might owe more than one person the same thing.

For instance, in climate justice we might say that we owe something to all of the people who are young now or haven't been born yet. In social justice you might owe something to a whole group of people. Just because they're groups doesn't mean the individual people that comprise the group dissolve into an abstract concept, even if that's how it might seem in our minds.

In some cases maybe the definition is too narrow because it depends on what is or isn't a "person" which we might define too narrowly. Do we owe things to animals? I'd say so, and I think most people would agree, depending on the animal. Do we owe things to plants? Maybe. Do we owe things to the planet Mars, assuming it's entirely devoid of life? I don't know, but I think it would offend people's sensibilities if we were to dump toxic waste all over it's surface, even if we were sure that humans are never going to settle there or use any of its resources. There's a view of climate justice that we owe things to the Earth directly rather than (or in addition to) owing something to the people that live there or will live there.

Gotcha. I did preface this definition with the word 'candidate' and I acknowledge that there may be good alternate formulations. The spirit of this particular exchange is about whether or not 'justice' can be formulated as a universal.

I shared an argument above for why it can be viewed as a universal and judging by your comment above you are somewhat skeptical of this claim.

If we shift the discussion to allow conceptions of 'justice' that move away from the classical tradition and include modern ideas like 'climate' justice or 'social' justice, I will revert to agreeing with your skepticism.

I don't think anyone can plausibly claim that these more marxist-oriented modern definitions are universals.